NMR Measurement of Intracellular Potassium in the Perfused Normotensive and Spontaneously Hypertensive Rat Aorta by a Multinuclear Subtraction Procedure

Intracellular free potassium ion concentrations have been measured in the isolated perfused aortae from Wistar-Kyoto and spontaneously hypertensive rats by a novel multinuclear NMR procedure, which allows the estimation and subtraction of the extracellular potassium signal from the total 39K+ resonance. When tested on a sample of erythrocytes, the method yielded an intracellular potassium concentration of 149 mmol/L cell water, which is similar to the previously reported average of 140 mmol/L cell water, indicating full (100%) NMR "visibility" of red cell 39K+. In contrast, the 39K+ resonance of the perfused rat aorta preparation indicated very low (approximately 15%) NMR visibility of intracellular potassium in the aortic tissue, similar to that previously reported for perfused hearts. More importantly, aortae from spontaneously hypertensive rats yielded a corrected (for low NMR visibility) intracellular potassium concentration of only 90 +/- 10 (mean +/- SE; n = 6) mmol/L cell water, which was significantly lower (40%; P = .02) than that in aortae from normotensive rats. The NMR data thus reveal a significant depletion of intracellular potassium in hypertensive arterial smooth muscle cells.